In order to connect electrodes of a semiconductor element to external leads, there has conventionally been used a wire made of Au alloy containing a small amounts of Ca, Be, Ge and etc. in a base of Au which wire has a diameter of 25 to 50 .mu.m, that is, the bonding wire has been used.
When such wire is used for connecting the semiconductor element and a lead frame to each other, such a method has been effected that both components are pressure-bonded through ultrasonic waves, or for the electrodes of the semiconductor element, a hot pressure bonding is effected after each tip thereof has been balled up by arc.
However, it has been recently achieved to make an IC smaller in size and to make the degree of integration thereof higher, with the result that there occurs such problem that, due to an increase in number of electrodes, the electrodes have occupied a too large area in the case of a conventional wire diameter. In order to solve this problem, it is necessary to make the diameter of wire small. However, in the case where the now available wire is made small in size, the wire is apt to rupture to high degree during a wiring operation and the use thereof. Such wire can not be used practically.
For this reason, it has been considered that, regarding the conventional wire, a wire diameter of about 20 .mu.m is the minimum.
There are some attempts to make a wire diameter small as disclosed in Japanese Patent Unexamined Publication Nos. 56-49534 and 56-49535 in which Pt of up to 30 wt % or Pd of up to 40% is added to Au to thereby enhance the strength of the wire and to make the wire diameter small. However, if the content of the alloy elements exceeds a certain limit, there occurs such problem that a hardness of the ball will be increased and a load necessary for hot pressure bonding will be increased with the result that a silicon chip of an IC is apt to be damaged. Japanese Patent Unexamined Publication No. 60-15958 proposes an Au base alloy wire as a bonding wire having a good hot pressure bonding property with respect to electrode wirings in which a different element is mixed into Al. This also suffers the same problem as above. Thus, there is a demand to provide a new bonding wire that is effective for making an IC small in size and densified in a higher degree without any special modification of the conventional IC and a conventional bonding method that have been used.